Look at the sentence below please and tell me why the writer of this sentence made what looks to be a choice to modify the nouns with an indefinite article.

This essay contain a beginning paragraph, a middle paragraph and an ending paragraph.

Would it be wrong to modify them all with a definite article, like this? I feel very strongly and am pretty sure (Ha ha) that there is only one beginning paragraph, one middle paragraph and one ending paragraph for this particular essay.

This essay contain the beginning paragraph, the middle paragraph, and the ending paragraph.

Obviously, including/having that phrase will make a big difference for the reader, but my question to you and all others is how many times do you see a sentence like that having the kind of phrase as you added? Not many I think.

Would you always want to say the crayon, the pencil and the piece of paper? We would use 'the' only if they are a specific crayon, pencil and piece of paper we already know about and need to emphasise that it really is those particular items, and not just any crayon, pencil and piece of paper.

When introducing the contents of something, the parts of something, or listing the components of something for the first time, we use the indefinite. That's because we are not referring back to each particular element of the list as a particular, unique object in the universe. We are only giving a generic idea of certain types of things.

Next to the plate were a knife, a fork, and a spoon. (No particular knife, fork, or spoon mentioned earlier.)The refrigerator contained a bottle of milk and a stick of butter. (Etc.) There was a paragraph at the beginning of the essay, a paragraph in the middle of the essay, and a paragraph at the end of the essay. Inside the house was a small kitchen. (No particular kitchen mentioned earlier.)The letter contains a reference to the prime suspect in the case. This box contains a key and a paper clip. The menu had a grouping for fish dishes, a grouping for chicken dishes, and a grouping for beef dishes.

The thrust?? of my inquiry lies with the article usage with such terms as "beginning" and "ending." Whenever I see a word preceded with such a term, instinctively I try to put the article "the" unless my close scrutiny shows it otherwise. I think my confusion is being further fueled by the fact that we normally associate a with the concept of one, in addition to the notion of it being an indefiite article, and when I see the sentence like the one below, it having a makes me concentrate too much on the "one" concept. Help me to set what seems to be a misguided perception straight.

Let me try a different kind of explanation. The first time you mention something to me, say 'a'. That makes the thing specific/definite in our conversation. So thereafter, you can say 'the' and I'll know the thing you are talking about.

Aman with a scar on his nose and a parrot sitting on his shoulder came into the room. The man sat down. Theman smiled at me.